Optical transmission systems may include a multitude of optical structures, referred herein also as optical elements or optical devices. Often, these optical circuits may increase in complexity as the optical transmission systems are designed to meet higher capacity demands. The optical structures of the optical circuits may be used, for example, to guide one or more propagating optical signals. Some of the optical structures may act to combine or split propagating optical signals. For example, an exemplary optical structure may be configured to receive first and second optical signals and combine the first and second optical signals such that one or more outputs of the optical structure includes a first percentage, or first power, of the first optical signal and a second percentage, or second power, of the second optical signal.
Optical structures which combine or split optical signals to provide desired outputs including desired powers of the input optical signals may provide such outputs based upon the specific geometry of the optical structure, for example the length and/or the width of the optical structure. Such optical structures may be harder to fabricate in a consistent manner, in order to duplicate the optical structures in a multitude of similar optical circuits as part of a semiconductor wafer for example. Due to fabrication variations for example, it may be difficult to consistently fabricate certain optical circuits to meet desired design criteria unless appropriate consideration is made in circuit layout and chip layout. Varying distances or gaps between adjacent optical structures of an optical circuit, as defined within or as part of an associated mask pattern used during fabrication for example, load the etch process differently. This may lead to inconsistent optical structures as compared to associated design specifications, or as compared with other similar optical structures which share the design specifications. Such optical structures may include, for example, multimode interference couplers, or other optical combiners or optical splitters, or other optical structures which provide outputs which are a function of the geometry of the optical structure, such as a width or a length of the optical structure for example. To ensure consistent manufacturability of certain optical circuits, the optical structures of the optical circuits may be positioned relatively far apart from adjacent optical structures of the optical circuits. However, this results in larger optical circuits and, ultimately, higher manufacturing costs.
There is a need for highly manufacturable compact optical structures in optical circuits. There is also a need to provide compact optical structures which lead to compact optical circuits and lower manufacturing costs.